Introduction to Transcription - Video Tutorials & Practice Problems
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concept
Introduction to Transcription
Video duration:
5m
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Video transcript
In this video we're going to begin our introduction to transcription. And so recall from our previous lesson video that DNA within a gene as the coding template, and so this is the process of building RNA. Now also recall from our previous lesson videos that genes are really referring to small units of DNA that encode a product, for example, a protein. And so genes, in order to create a protein, will need to be both transcribed and translated. And so here we're talking about the first step of the process, which is transcription, being transcribed. Now in order to better understand transcription, it's helpful to, describe some specific sequences of DNA that mark where transcription of a gene begins and ends. And so, the first, sequence of DNA that you should note is called the promoter. And so the promoter is a small stretch of DNA sequences where transcription begins. And so the promoter is really just the site where the RNA polymerase is going to attach, and the RNA polymerase, is going to be the primary enzyme involved in transcription. And so the RNA polymerase, as we're mentioning down below here, is going to be an enzyme, the primary enzyme that is going to polymerize or build RNA from scratch. And, turns out that RNA polymerases do not need a primer like DNA polymerases do. And so RNA polymerase does not require a primer. And, again, we're going to talk a lot more about RNA polymerase and transcription as we move forward in our course here. But it's important to note that the promoter is going to be the sequence where transcription begins because this is the site where the RNA polymerase first attaches. Now the terminator, on the other hand, is also going to be a stretch of DNA sequences, but this is where transcription is going to end. And so if we take a look at our image down below, what you'll notice is on the far left, we have a chromosome, a replicated chromosome, which we know consists of DNA and protein. But if you unravel this chromosome, what you'll find is there is DNA in here, and some of these DNA, some of this DNA are going to be genes. They encode a product like a protein. And so if we take a look at a typical gene, and zoom into it, what you'll find is that it's going to have a, green region here that we're going to be referring to as the promoter. And the promoter is, again, the small stretch of DNA sequences that allows for the RNA polymerase to bind. And this pink structure that you see here is the RNA polymerase. This is the primary enzyme involved with transcription. And so the RNA polymerase, what it does is it will bind to the gene specifically at this promoter region, and then the RNA polymerase will transcribe the coding sequence of this gene. And then, the terminator over here at the end is, of course, where transcription is going to end. And, collectively, the promoter, the coding sequence, and the terminator, basically, this entire region right here, is referred to as the gene. Now sometimes there are other important sequences that surround a gene, and so it's important to be able to refer to the directionality of those sequences that might be outside of the gene. And what they use are the terms upstream of the gene and downstream it turns out that downstream of the gene is referring to DNA sequences in the same direction as transcription. And so you can see the arrow down here. You can think of little fishies downstream, and the downstream is going to represent, DNA sequences outside of the gene that are in the same direction of transcription. And in this case, because the RNA polymerase binds here, it's going to be transcribing in this direction, and so downstream is in the same direction of transcription. Now the opposite direction is going to be referred to as upstream. And so upstream is going to refer to DNA sequences in the opposite direction of transcription. And so, again, the RNA polymerase is binding at the promoter and transcribes in this direction, but upstream of the gene is going to be in the opposite direction of the transcription direction. And so this here concludes our brief introduction to transcription. And as we move forward in our course, we're going to continue to learn more and more about transcription. So I'll see you all in our next video.
2
Problem
Problem
Which of the following is the best definition of a gene?
A
An RNA molecule transcribed from a sequence of DNA.
B
A stretch of DNA that can be transcribed.
C
A sequence of DNA where the process of transcription ends.
D
A sequence of DNA that encodes a product like an RNA or a protein.
E
A sequence of DNA where the process of transcription begins.
3
Problem
Problem
Which of the following statements is false?
A
Transcription is the process that creates an RNA product from a sequence of DNA.
B
RNA polymerase builds RNA molecules from a DNA template.
C
A promoter is a sequence of DNA within a gene where RNA polymerase can begin transcription.
D
RNA polymerase, like DNA polymerase, requires a primer to begin RNA synthesis.
4
concept
Overview of Transcription
Video duration:
7m
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Video transcript
In this video, we're going to do an overview of the entire process of transcription. However, it's important to keep in mind that as we continue to move forward in our course, we're going to continue to continue to move forward in our course, we're going to continue to break down transcription in more details. And later in our course in a separate video, we'll talk about the individual steps of transcription in more details. And here in this video, we're just doing an overview of the entire process. And so it's important to note that the two strands of DNA in a gene are referred to as either the coding strand or the template strand. Now, turns out that during transcription, the RNA molecules that are being built are going to have the same exact sequence as the coding DNA strand. And the template DNA strand is just going to serve as a template for building the RNA. But ultimately, the RNA molecule is gonna be carrying the message that's in the coding DNA strand. And so the only difference between the RNA sequence and the coding DNA sequence is going to be the fact that it's going to be replacing all of the t's or thymines with u's or uracils. And recall that is because RNA has uracils, whereas DNA is going to have thymeins. And we'll be able to see an example or an application of this down below in our example. Now it's also important to note that during transcription, the RNA molecule itself is going to be built from its 5 prime end to its 3 prime end, and it's going to be built by pairing free RNA nucleotides that are floating around in the cell on a DNA template. And so we'll be able to see that down below in our image over here on this side. Now this nucleotide pairing is going to occur via Watson and Crick base pairing, which, recall, we already covered in our previous lesson videos, which basically says that a's or adenines will pair with t's or thymines. Or in the case of DNA base pairing with RNA, a's are going to be base pairing with u's, because remember that in RNA, u's are going to replace the t's. And then, of course, we know that g's are going to base pair with c's. And so if we take a look at our image down below, we can, better understand template DNA template DNA strand and for the mRNA transcript given the following coding strand. And so when we take a look at this side of the image over here, what you'll notice is we have a DNA molecule. And recall that DNA has 2 strands, and each of these two strands, one of them is going to be the coding strand and the other one's going to be the template strand. In this case, the coding strand is at the top here and the template strand is the one on the bottom. And so it wants us to determine the template DNA strand sequence along with the mRNA transcript sequence that's down below. And so, what's important to note here is that, when we look at the coding sequence, coding strand sequence, it is g g a t c, and we know that through Watson and Crick base pairing that the g's are going to base pair with c's, and so these g's here will base pair with c's on the DNA. So we know that c's are going to go in these positions and that a's are going to base pair with t's in the DNA. And so, we will put t's here, and t's will base pair with a's, and, of course, c's base pair with g's. And so this sequence here is the sequence of the template strand sequence. Now, of course, the process of transcription represented by this arrow is going to use the DNA to build RNA. And, the RNA, as we mentioned up above, are going to have the same sequence as the coding DNA strand with this exception right here, replacing the t's with u's. And so what we can see here is that the coding sequence strand is right here at the top, and RNA is going to have the same sequence as the coding strand. So it is going to be g g a, and then, of course, replacing the t's with u's, as we mentioned here, replacing the t's with u's. And so here, instead of having a t at this position, we're going to have a u. And then, of course, the c here is gonna go right here. And so this will be the sequence of the RNA. Now it turns out that in eukaryotic cells, the RNA that is first made is called a pre mRNA transcript because it's not fully mature, but we're going to talk more details about that later in our course. Now over here on the right, we're kind of showing you more of a zoom out of the overall process of transcription. And recall that the RNA polymerase enzyme, which is this big pink circle in the background, is the primary enzyme involved with transcription. And so it will bind to the promoter region on a gene and start to transcribe the gene. And so when it transcribes a gene, it's going to be building the RNA, and the RNA is gonna be built from its 5 prime end to its 3 prime end, again, by pairing free RNA nucleotides that are floating around in the cell on a DNA template. And so you can see that this RNA is being built from its 5 prime end over here towards its 3 prime end over here. And the direction of, the RNA polymerase is to the right, so transcription is proceeding to the right. And so what you'll notice is that the DNA is going to unwind, and you can see that there's a coding strand and, again, a template strand. And, the RNA, of course, is going to end up taking the same exact sequence as the coding strand. And again, this this bottom one that's down here is going to be the template strand of DNA. Now you'll notice that there is going to be a region here highlighted by this box, which is represented, representing an RNA DNA hybrid region. And so, you can see that these free RNA nucleotides that are floating around in the cell are going to be incorporated into this RNA molecule by the RNA polymerase enzyme. And so this here is representing the overall overview of of transcription. And, again, as we move forward in our course, we're going to break down this process of transcription in more details, looking at it step by step by step. But for now, this here concludes our overview of transcription, and we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you all in our next video.
5
Problem
Problem
The strand of DNA that has the same sequence as the RNA molecule being created during transcription is the:
A
Lagging strand.
B
Leading strand.
C
Coding strand.
D
Template strand.
E
Parent strand.
6
Problem
Problem
Transcription is sometimes described as a process in which RNA is "copied" from the template strand of DNA. This statement is potentially misleading since _____.
A
The nucleotides in RNA contain ribose and cannot be an exact copy of DNA.
B
RNA molecules contain uracil instead of thymine and cannot be an exact copy of DNA.
C
The RNA transcript has a sequence complementary to the template.
D
The RNA transcript and the DNA template strand are antiparallel.
E
All of the above.
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